1. Field of the Invention
The present invention relates to a zoom lens system and an image pickup apparatus including the same.
2. Description of the Related Art
In recent years, there has been a demand for a zoom lens system having both a high zoom ratio and a high optical performance for image pickup apparatuses such as television cameras, digital cameras and video cameras.
Positive lead type four-unit zoom lens systems in which four lens units are provided in total with the one of the lens units located closest to the object side having a positive refractive power have been known as zoom lens systems having a high zoom ratio (Japanese Patent Application Laid-Open No. 2003-287678 and Japanese Patent Application Laid-Open No. H08-146294). In such four-unit zoom lens systems, an optical material which has extraordinary dispersion or a diffraction element is used to correct for chromatic aberration.
However, along with a higher zoom ratio of the zoom lens system and a higher definition of an image pickup element, higher performance of the zoom lens system, in particular, further reduction in axial chromatic aberration over the entire zoom range is demanded.